Prostaglandins (PG s) appear to have a major role in the initiation and/or maintenance of parturition. Inhibition of prostaglandin synthesis is used as a mechanism of tocolysis in preterm labor, though not without potentially deleterious side effects for the fetus. The response and sensitivity of myometrium to PG's may be governed by differential expression of various PG receptors, many of which have been recently cloned and sequenced. The PG receptors are part of the superfamily of G protein-coupled receptors that have seven transmembrane spanning domains. Each prostaglandin species has a specific receptor isoform linked to a distinct signal transduction pathway giving contraction or relaxatory responses. Alternate splicing of receptor mRNA transcripts give rise to isoform subtypes that can be linked to different signal transduction pathways with diverse actions. Hence, the response to any particular prostaglandin (e.g. PGE2) may depend on the receptor isoforms and their subtypes expressed at any particular time. The receptor isoforms present in myometrium have previously been characterized by pharmacologic means. The recent cloning and sequencing of these receptors offers the opportunity to critically study isoforms and subtypes present, their ontogeny throughout gestation and changes with parturition and hormonal manipulation. Unfortunately, specific antibodies and probes to the receptor isoforms are not available. A principal objective of this proposal is to develop reagents to facilitate these studies. The overall hypothesis to be tested is that uterine responsivity to prostaglandins is in part regulated by differential expression of contractile and relaxatory PG receptor isoforms in myometrium and that this expression is hormonally regulated by estrogen/progesterone. The three objectives of the study are to (1) identify and synthesize unique peptide sequences for each receptor isoform to raise antibodies for immunohistochemistry and western blotting studies (2) isolate cDNA s for selected receptor isoforms from rat and human, myometrium for use in in situ hybridization and northern analysis and (3) study the regulation of receptor isoforms in pregnant rat myometrium by manipulation of estrogen and progesterone synthesis and action. Description of the occurrence, ontogeny and regulation of PG receptors in myometrium is a crucial first step in beginning to explore the use of stimulation of inhibition of specific receptors as a novel selective means of tocolysis. A necessary first step is the development of quality reagents to aid in this study and for further use in probing receptor structure/function relationships.